The present invention relates to improvements in devices injecting plastics material in a mould having a plurality of impressions.
Injection moulding machines are already known which generally comprise a distribution plate pierced with channels for the inlet of the molten plastics material and provided with heating means to maintain this plate at a relatively high temperature, of the order of 200.degree. C. The plastics inlet channels communicate with the injection nozzles which are respectively associated with the individual moulds in which the injection is to take place and which each comprise an impression insert housed in an impression plate provided with a cooling circuit, to maintain it at a temperature much lower than the distribution plate, of the order of 40.degree. C. In each injection nozzle is slidably mounted a needle forming obturator, normally obturating an injection orifice provided at the end of the nozzle and through which the plastics material may be injected into each mould.
In the heretofore known injection moulding machines, the distribution plate bearing the injection nozzles and the impression plate are assembled together with considerable mechanical forces, obtained by means of set screws, being given the very high pressure of injection employed. Now, these high mechanical forces are incompatible with the expansions or contractions which appear in the course of production due to the permanent contact of the hot distribution plate with the cold assembly constituted by the impression plate. The tightness obtained under these conditions is particularly doubtful and furthermore the corrections of the axial alignments are obtained by providing a longer length of the constituent elements, this therefore allowing a certain flexion thereof.
Consequently, the central obturator provided in each injection nozzle is never in line with the injection orifice, hence its destruction with loss of appearance of the injection threshold on the moulded piece.
The above construction also leads to very considerable dimensions of the mould.